There has been proposed the method for forming color images on a thermal transfer image-receiving sheet which is dyeable with a sublimable dye by using a thermal transfer sheet composed of the sublimable dye as a recording agent and a substrate on which the sublimable dye is supported. In this method, the dye is heated using a thermal head of a printer as a heating means and transferred on the image-receiving sheet to obtain the color images. The thus formed images are very clear and excellent in transparency because of the dye used, and are therefore expected to provide high-quality images which are excellent in reproducibility of half tones and gradation.
In the thermal transfer image-receiving sheets, polyesters are used in a dye receptor layer thereof from the viewpoint of an excellent dyeability of the thermal transfer image-receiving sheets with dyes. It is known that an alkyleneoxide adduct of bisphenol A is employed as a raw monomer of the polyesters. For example, there is disclosed a thermal transfer image-receiving sheet in which a dye receptor layer contains a polyester resin produced from a dicarboxylic acid component containing 40 mol % or more of an alicyclic dicarboxylic acid compound and a diol component containing 15 mol % or more of a diol compound having a bisphenol A skeleton as a dye acceptable resin (JP 2002-19306A). On the other hand, there has been proposed a method in which a styrene resin or an acrylic resin is used in a dye receptor layer of a thermal transfer image-receiving sheet from the viewpoint of a good releasability of the sheet (JP 2002-283750A).
Further, there is known a technique in which a mixed resin of polyester and a thermoplastic resin such as polystyrene, or a resin having a main chain composed of a polyester having an unsaturated bond and a side chain composed of a polymer of a radical polymerizable unsaturated monomer is used in a dye receptor layer (JP 6-24156A and JP 10-60063A). In addition, there is disclosed a technique in which resins that are different in glass transition point from each other are used from the viewpoint of attaining a good image density (dyeability) (refer to JP 2007-229987A).